1. Field of the Invention
The invention relates to a tool clamping device and a tool clamping method.
2. Description of the Related Art
At present, a two-face restraint clamping system for a hollow tapered tool, such as an HSK system conforming to Japanese Industrial Standards (JIS) or a KM system conforming to manufacturer standards, for example, is available as a tool clamping system for an automatically exchangeable tool exhibiting a high degree of repeat attachment precision.
According to a tool clamping device described in Japanese Patent Application Publication No. 2005-313311 (JP-A-2005-313311), a clamping mechanism for clamping a pull stud portion formed on a taper shank portion of a tool holder is housed in the interior of a unit main body, and a draw bar connected to a slider for open/close operating a clamping member of the clamping mechanism is caused to project to the outside from a rear end portion of the unit main body. A belleville spring is mounted on an outer periphery of the draw bar so as to be positioned between a spring receiving member and a spring receiving member, and thus the draw bar is normally biased in a rearward clamping direction. In this clamped state, a spindle restrains the taper shank and an end surface of the tool holder, thereby realizing so-called two-face restraint clamping.
However, a clamping mechanism of an HSK system or another two-face restraint clamping system for a hollow tapered tool, which is used in the tool clamping device described above, is shaped to provide a tool taper portion with a tightening margin, and therefore, when a pull-in force (clamping force) is caused to act, the hollow taper portion of the tool itself and a partner spindle taper portion are deformed by an amount corresponding to the tightening margin, whereby positioning is performed in a centering direction while keeping the tapered surfaces in close contact. From this state, end surfaces are pulled into close contact through deformation corresponding to the tightening margin, whereby positioning is performed in an inclination direction. The clamping operation is thus complete. In other words, centering direction positioning and inclination direction positioning are performed simultaneously mainly using only an axial direction pull-in force. As a result, the centering precision, which contributes greatly to tapered surface positioning in a geometrical sense, is favorable, but the inclination precision, which contributes greatly to end surface positioning, is poorer than the centering precision, leading to variation in the precision of repeat tool attachment.